Chapter 19~ The Organization and Control of Eukaryotic Genomes

Chromatin

Def: complex of DNA and proteins

DNA Packing •histone protein (+ charged amino acids ~ phosphates of DNA are - charged)

Nucleosome •”beads on a string”; basic unit of DNA packing

Heterochromatin •highly condensed interphase DNA (can not be transcribed)

Euchromatin •less compacted interphase DNA (can be transcribed)

DNA Packing

Repetitive DNA (Satellite DNA)

Repeating units of DNA

Normally not coded

Can cause problems: Huntington’s disease, fragile X syndrome.

Found in centromeres and telomeres

May be tandem or interspersed

Classified according to length: regular, minisatellite, microsatellite

Gene Expression-
Eukaryotes

Transcription/RNA Processing

Control of Gene Expression

Cell differentiation is determined by the selection of genes expressed in the cell

Can occur at any point in the metabolic pathway of protein synthesis

Chromatin modifications

Organization of chromatin determines which genes will be transcribed

DNA methylation: tends to pack DNA and turn genes “off” (-CH 3)

Histone acetylation: acetylation loosens the “grip” of histone to DNA (expands it), deacetylation tightens the grip. (-COCH 3)

Transcription Initiation

Eukaryotic genes have introns (non-coding segments)

These regulate transcription by binding to trancription factors.

Transcription factors: group of molecules that enhance transcription

Post Transcription Control

Alternative RNA splicing

mRNA degradation regulation

Control of translation

Protein processing and degradation

Molecular Biology of Cancer

Oncogene •cancer-causing genes

Proto-oncogene •normal cellular genes

Genes change via:

1-movement of DNA; chromosome fragments that have rejoined incorrectly

2-amplification; increases the number of copies of proto-oncogene

3-proto-oncogene point mutation ; protein product more active or more resistant to degradation

Tumor-suppressor genes

- changes in genes that prevent uncontrolled cell growth (cancer growth stimulated by the absence of suppression)